In an analog telephone network, a pair of wiresxe2x80x94the tip and ring linesxe2x80x94are used to connect a subscriber""s telephone to the central office (CO). To test the network, sometimes an automated test system is used; a mechanized loop tester (MLT) is an example of such a test system. The MLT is connected to a central office switch and is connected through the switch to the line pair under test. On plain old telephone service (xe2x80x9cPOTSxe2x80x9d) line pairs, the MLT performs a series of automated tests, which include measurements for shorts, opens, resistive faults and foreign voltages, etc.
With the introduction of digital loop carrier (DLC) systems, multiple phone channels are multiplexed onto a line pair. This practice is known as adding pair gain. A DLC system, based on HDSL (high-bit-rate digital subscriber line) technology, is shown in FIG. 1. A central office 10 includes a CO switch 12 and a central office line unit (COLU) 14. In the example of FIG. 1, four line pairs from the CO switch are input to the COLU 14.
The COLU is coupled to a remote line unit (RLU) 16 via a single pair of copper wires, labeled HDSL pair. The HDSL pair is an ordinary pair of copper wires. However, high speed data rates (e.g., 784 Kbps in each direction) are achievable by HDSL technology. HDSL utilizes digital signal processing techniques to create a mathematical model of the HDSL copper pair and compensate for the distortion imparted on the signal by the copper line pair. At the RLU 16, the digital signal is demultiplexed and converted into analog signals corresponding to those which originated at the CO switch 12. The analog signals are supplied to the subscribers"" telephones. In this example, one pair of copper wires (the HDSL pair) is used to provide a high speed transmission path for four separate telephone channels.
Testing of the FIG. 1 system is complicated by the fact that there is not a direct analog connection between the CO switch and a subscriber""s line. To test the DLC channel, a pair gain test controller (PGTC) is used. A MLT is still used to test the wire pairs beyond the DLC devices.
The mechanized loop tester (MLT-2) 18 is coupled via the trunk tip, trunk ring and trunk sleeve lines to the pair gain test controller 20, which includes a channel tester 22. To test the analog portion of the system, the trunk tip and trunk ring lines are coupled, at the PGTC 20, to a bypass pair 24, via a switch (not shown). When the MLT is connected to the bypass pair 24, the MLT is not coupled to additional circuitry. The bypass pair is coupled, at the RLU 16, to the POTS pair under test. That is, there is a direct analog connection between the MLT 18 and the subscriber""s telephone being tested. Through such a connection, the MLT measures for shorts, opens, etc.
To test the digital portion of the network, the channel tester 22 in the PGTC 20 is coupled via the tip, ring and sleeve lines to a Numbered Test Trunk (No Test Trunk) 26. The No Test Trunk 26 and the central office switch 12 connect the tip and ring lines to a selected one of the POTS pairs, which in turn are multiplexed by the COLU 14 onto the HDSL pair. If the digital portion of the network is satisfactorily connected to the PGTC, the PGTC 20 places a 1 Kxcexa9 resistance value between the trunk tip and trunk ring lines which is interpreted by the DCTU as a signal that testing is to proceed. The HDSL pair is coupled to the RLU 16 which demultiplexes the test signals on the HDSL pair for the POTS line under test.
Test information about the digital portion of the network obtained by the PGTC 20 is provided to the MLT 18. That information, along with the analog line test result information obtained directly by the MLT is provided to a service technician for analysis of the test results, and, if needed, corrective action. See generally specification TR-TSY-00465 published by Bellcore.
FIG. 2 illustrates a system wherein the functions of the mechanized loop tester are integrated into the central office switch. This is referred to a I-MLT-2. In the integrated testing situation, a direct connect test unit (DCTU) 30 within the central office switch 12 controls the testing operations.
For an analog, i.e., non-DLC, network, the DCTU 30 is coupled through a modular metallic switch unit (MMSU) 32 to a line unit (LU) 34. The line unit 34 is coupled to the POTS line under test.
In a DLC network, the DCTU is coupled through the MMSU 32 to the trunk tip, trunk ring and trunk sleeve lines, which are in turn coupled to the pair gain test controller 20. To test the digital portion of the network, the channel tester 22, within the PGTC 20, is coupled via the tip and ring lines back through the MMSU 32, over to the line unit 34, and then to the POTS line under test. There is no connection for the sleeve line out of the PGTC 20. The POTS line is coupled to the COLU 14 which in turn is coupled to the RLU via the HDSL pair. If the digital portion of the network is satisfactorily connected to the PGTC, the PGTC 20 places a 1 Kxcexa9 resistance value between the trunk tip and trunk ring lines which is interpreted by the DCTU as a signal that testing is to proceed.
As with the non-integrated case, the network beyond the DLC is tested using the bypass pair 24. The trunk tip and trunk ring lines are coupled to the bypass pair 24 via switches (not shown) within the PGTC 20. During such test, the channel tester 22 is isolated from the trunk tip and trunk ring lines. Like the MLT in the non-integrated case, the DCTU 30 measures for shorts, opens, resistive faults and foreign voltages on the subscriber""s line under test.
A major draw back of the FIGS. 1 and 2 systems is that for testing, a bypass pair 24 is required for every COLU/RLU pair. In other words for every HDSL pair, a bypass pair is required for testing purposes. This significantly lessens the extra line capability provided by the digital loop carrier system. Often, crafts personnel xe2x80x9cborrowxe2x80x9d the bypass pairs to correct other service problems and thus, they are not available when needed for testing.
A further disadvantage of the prior integrated testing technique is increased cost resulting from the need to provide an interface within the DLC to the PGTC.
Accordingly, it is an object of the present invention to provide a digital loop carrier system which does not require the use of a bypass pair for testing purposes.
It is an additional object of the invention to lessen DLC system costs by allowing a pair gain test controller to remain idle during testing, yet have a satisfactory system pass testing.
In accordance with the invention, a conditioner unit for a pair gain test controller is provided. The PGTC conditioner unit (PCU) is coupled to the PGTC via the sleeve line and the trunk ring line. The PCU senses a signal which indicates that the DCTU is seeking test results from the PGTC, and provides a signal which indicates to the DCTU that the PGTC test results are satisfactory, even though the PGTC remained idle.